Python code for Edge Data Bevel and Crease Weight?
EDITED:

OK, apparently the previous answer was pretty worthless. Although there is a meshedge.crease property and a meshvertex.bevel_weight property, they do not influence modifiers at all, and their values do not change when changing the corresponding values in the properties panel.

However, there is a way to access these values through custom layers via BMESH. The addon below adds a panel that allows you to influence selected verts / edges or all verts / edges' crease and bevel weight properties.



It does have one weird bug though, which seems to be a bug in Blender, as seen in the GIF above. Even though this does indeed update the respective mesh properites, Blender does not update the display until you also change any value of a modifier on the active mesh.

EDITED 2:

Thanks to a comment from batFINGER, found a solution to the weird behavior mentioned and seen above: adding a bmesh.update_edit_mesh( meshData ) after updating the crease / bevel values. Updated code below accordingly.

To use this, download the code and save it as a python (.py) file on your computer, then install it as an addon (File --> User Preferences --> Add-ons --> Install From File).

The panel appears in Edit Mode only in the Tools tab, under "Crease and Bevel".

bl_info = {
    "name"       : "Crease and Bevel weight panel",
    "version"    : (0, 0, 1),
    "blender"    : (2, 77, 0),
    "category"   : "Tools",
    "location"   : "3D View &gt; Toolbox",
    "description": "Shortcut UI panel for Mesh edge crease and vertex bevel weight properties"
}

import bpy, bmesh

class creaseAndBevelPanel(bpy.types.Panel):
    bl_idname      = "creaseAndBevelPanel"
    bl_label       = "Crease and Bevel"
    bl_space_type  = 'VIEW_3D'
    bl_region_type = 'TOOLS'
    bl_category    = 'Tools'
    bl_context     = "mesh_edit"

    @classmethod
    def poll( self, context ):
        ''' Only show panel if there is an active mesh object '''
        return context.object and context.object.type == 'MESH'

    def draw( self, context ):
            layout = self.layout
            props  = context.scene.creaseAndBevelPG # Create reference to property group

            box = layout.box()                    # Draw a box
            col = box.column( align = True )      # Create a column
            col.prop( props, "whoToInfluence"  )  # Add properites to panel
            col.prop( props, "bevelWeight"     )
            col.prop( props, "edgeCrease"      )

class creaseAndBevelPG(bpy.types.PropertyGroup):
    ## Update functions
    def update_bevelWeight( self, context ):
        ''' Update function for bevelWeight property '''

        o  = bpy.context.object
        d  = o.data
        bm = bmesh.from_edit_mesh( d )

        bevelWeightLayer = bm.verts.layers.bevel_weight['BevelWeight']

        if self.whoToInfluence == 'Selected Elements':
            selectedVerts = [ v for v in bm.verts if v.select ]
            for v in selectedVerts: v[ bevelWeightLayer ] = self.bevelWeight
        else:
            for v in bm.verts: v[ bevelWeightLayer ] = self.bevelWeight

        bmesh.update_edit_mesh( d )

    def update_edgeCrease( self, context ):
        ''' Update function for edgeCrease property '''

        o  = bpy.context.object
        d  = o.data
        bm = bmesh.from_edit_mesh( d )

        creaseLayer = bm.edges.layers.crease['SubSurfCrease']

        if self.whoToInfluence == 'Selected Elements':
            selectedEdges = [ e for e in bm.edges if e.select ]
            for e in selectedEdges: e[ creaseLayer ] = self.edgeCrease
        else:
            for e in bm.edges: e[ creaseLayer ] = self.edgeCrease

        bmesh.update_edit_mesh( d )

    ## Properties
    items = [
        ('All', 'All', ''),
        ('Selected Elements', 'Selected Elements', '')
    ]

    whoToInfluence = bpy.props.EnumProperty( # Material distribution method
        description = "Influence all / selection",
        name        = "whoToInfluence",
        items       = items,
        default     = 'Selected Elements'
    )

    bevelWeight = bpy.props.FloatProperty(
        description = "Bevel Weight",
        name        = "bevelWeight",
        min         = 0.0,
        max         = 1.0,
        step        = 0.01,
        default     = 0,
        update      = update_bevelWeight
    )

    edgeCrease = bpy.props.FloatProperty(
        description = "Edge Crease",
        name        = "edgeCrease",
        min         = 0.0,
        max         = 1.0,
        step        = 0.01,
        default     = 0,
        update      = update_edgeCrease
    )

def register():
    bpy.utils.register_module(__name__)
    bpy.types.Scene.creaseAndBevelPG = bpy.props.PointerProperty( type = creaseAndBevelPG )

def unregister():
    bpy.utils.unregister_module(__name__)